The present invention relates to a method and apparatus for determining the concentration of a monitored gas in a medium in a storage vessel and, more particularly, the concentration of hydrogen sulfide gas in storage facilities for storing hydrocarbon products including petroleum products.
Hydrogen sulfide gas is a colorless, naturally occurring gas which is co-produced with many of the world's crude oils. Hydrogen sulfide gas is a particularly deadly gas. It has been found that concentrations of hydrogen sulfide gas of above 320 ppm have led to unconsciousness and even death. Oil companies, utilities and the like must contend with the problem of hydrogen sulfide gas which results in storage facilities where crude oils are held. The deadly gas collects in the vapor spaces or head spaces of oil tankers, barges, trucks, storage tanks, rail cars and the like. The release of hydrogen sulfide gas can become a dangerous problem during the transportation and storage of petroleum products as the concentration of the hydrogen sulfide gas can increase significantly under certain conditions. For example, research has shown that hydrogen sulfide concentrations increase in fuel oils due to the fact that the oils must be stored and transported at relatively high temperatures, that is, at temperatures of between about 120.degree. F. to about 180.degree. F. During the transportation of the oil the cargo tends to be agitated which further increases the likelihood of the release of gas during transport. It has been found that for every increase in temperature of about 40.degree. F. to 45.degree. F. in the residual oil during storage and/or transport, the concentration of the H.sub.2 S gas released may be doubled.
There is a growing awareness of the environmental concerns involved with emissions of H.sub.2 S gas. As a result, product specifications are subject to close scrutiny. It is imperative that the supplier of petroleum products as well as the purchaser of same be able to determine with accuracy the concentration of the poisonous H.sub.2 S gas in the product being bought and sold. While there are readily available mechanisms for analyzing the concentration of H.sub.2 S gas in a particular medium at one point in time, there has yet to be developed a system for predicting the levels of hydrogen sulfide gas in a product after transportation and storage at a given temperature.
Naturally, it would be highly desirable to provide a system and method for determining the concentration of a monitored gas in a medium and particularly hydrogen sulfide in petroleum products and to be able to predict the levels of hydrogen sulfide in a petroleum product under varying temperature conditions.
Accordingly, it is the principal object of the present invention to provide a method for determining the maximum concentration of a monitored gas in the head space of a confined space containing a medium such as a hydrocarbon medium or other media at a given temperature.
It is a further object of the present invention to provide a method as aforesaid wherein the equilibrium constant between the liquid phase and the gas phase of a medium contained in a confined space can be determined for any temperature.
It is a still further object of the present invention to provide a method as aforesaid wherein the actual concentration of the monitored gas can be determined at any temperature.
It is a particular object of the present invention to provide a system for carrying out the methods as aforesaid which is readily usable in the field.
It is another object of the present invention to provide an apparatus for extracting samples of a medium from a storage vessel and maintaining the samples under controlled temperature conditions for later analysis at that temperature.
Further objects and advantages of the present invention will appear hereinbelow.